In recent years, there has been an increased focus on reducing emissions of greenhouse gases generated by burning fossil fuels. One solution for reducing greenhouse gas emissions is developing renewable sources of energy. Particularly, energy derived from the wind has proven to be an environmentally safe and reliable source of energy, which can reduce dependence on fossil fuels.
Energy in wind can be captured by a wind turbine, which is a rotating machine that converts the kinetic energy of the wind into mechanical energy, and the mechanical energy subsequently into electrical power. Common horizontal-axis wind turbines include a tower, a nacelle located at the apex of the tower, and a rotor that is supported in the nacelle by means of a shaft. The shaft couples the rotor either directly or indirectly with a rotor assembly of a generator housed inside the nacelle. A plurality of wind turbines generators may be arranged together in a wind park or wind power plant to generate sufficient energy to support a grid. The rotor comprises one or more blades attached to a rotor hub. Each of the blades may be arranged to pitch relative to the hub, along a longitudinal axis of the blade.
Most modern wind turbines are controlled and regulated continuously, most often with the purpose of ensuring maximum power extraction from the wind under the current wind, and weather, while at the same time ensuring that the loads on the different components of the wind turbine are at any time kept within acceptable limits. Desirably, the wind turbine may also be controlled to account for fast sudden changes in the wind velocity the so-called wind gusts, and take into account the dynamic changes in the loads on the individual blades due to e.g. the passing of the tower, or the actual wind velocity varying with the distance to the ground (the wind profile or shear).
To this purpose a number of parameters are collected and monitored by the controllers in a wind turbine, such as for instance the current wind speed and direction, the rotational speed of the rotor, the pitch angle of each blade, the yaw angle, information on the grid system, and measured parameters (e.g. stresses or vibrations) from sensors placed e.g. on the blades, the nacelle, or on the tower.
Based on these and following some control strategy the optimal control parameters of the turbine in order to perform optimally under the given conditions are determined. The current performance, and thereby the power production and the load situation of the wind turbine is primarily controlled by controlling the pitch angles of the blades, but may further include adjusting for instance any different active aerodynamic devices for changing the aerodynamic surfaces of the blades such as flaps or vortex generating means, adjusting the power, and/or adjusting the rotational speed of the rotor.